<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 交集选择器 标签名.类名#id名 */
    span.aa::after{
      content: "水电费水电费";
    }

  </style>
</head>
<body>
  <p>我是p1</p>
  <p class="aa">我是p2</p>
  <span class="aa" >span</span>
  <div>div2</div>
</body>
</html>